It is known to provide a nondispersive infrared gas analysis device with a sample container for a gas which is to be analyzed wherein the receiver arrangement is subdivided into two separate layers which are formed to contain the same fluid and which are penetrated successively by a beam of radiation after the beam has passed through the sample container and wherein the height, in the direction of passage of the radiation, of a first receiving chamber containing the first receiving layer is several times smaller than the height of a second receiving chamber containing the second receiving layer. The purpose of this construction is to obtain better stability whenever the gas mixture to be analyzed does not contain the gas component, the existence of which is to be determined. This is shown in German Patent No. 10 17 385.
As an improvement on this device, especially in the case of trace analysis, a further nondispersive infrared gas analysis device is known wherein two adjacent containers are provided, one to contain the mixture to be analyzed and the other to contain a reference substance. The apparatus also includes an arrangement for the production of two substantially identical counter-phase modulated beams of rays which alternatingly pass through the mixture to be analyzed and the reference substance, and a single ray, two-layer receiver with two separate successive receiving two-layer receiver with two separate successive receiving chambers. As in the first case, this arrangement of the two successive receiving chambers lying in the path of rays also serves to achieve a sufficiently constant zero value, and is shown in German Patent No. 13 02 592.
Another known nondispersive infrared gas analysis device has a separate unidirectional path of the measuring and comparison rays and contains two receiving layers of variable length disposed in the same sequence successively in each path of rays and wherein both the energy difference between the absorbed energies of the receiving layers acted upon first by the radiation as well as the energy difference between the absorbed energies is formed in the receiving layers acted upon last by the radiation, and the corresponding electrical signals are then connected in opposition. This is shown in German Auslegeschrift No. 11 09 418.
Yet another nondispersive infrared gas analysis device includes separate paths for measuring and reference rays and includes two receiving chambers of variable length lying successively in each ray path. In this apparatus, the energy difference is determined between the pertinent sums of the absorbed energy of the receiving chamber acted upon first in one ray path and of the receiving chamber acted upon last in the other ray path. In this device, as in the previously described devices of the prior art, the purpose of the arrangement is to obtain an exact zero point, this being shown in German Auslegeschrift No. 16 98 218.
Finally, the prior art includes a nondispersive infrared gas analysis device with separate paths for measuring and reference-rays and with means for measuring the difference of the radiation energies absorbed in the receiving chambers. For the purpose of compensating for fluctuations in pressure, produced by shocks and accelerations of the mass of gas in the receiving chambers and their connecting lines, which fluctuations are superposed as interfering signals on the actual measuring signal, two additional gas filled chambers which are not acted upon by the radiation are provided, these chambers being assigned to the detector chambers in the paths for the measuring and comparison rays, the additional chambers being connected crosswise by gas conducting conduit. This is shown in U.S. Pat. No. 2,555,327.
The two layer receiving chambers used in these prior art gas analysis devices wherein the two receiving layers are penetrated by the radiation are dimensioned such that the receiving layer penetrated last by the radiation is longer than the receiving layer penetrated first by the radiation. With that relationship of the two layer receiving chambers, a particularly stable zero point results.
It has been found that although the devices of this type do have a satisfactory zero point character, they have the disadvantage of being "cross-sensitive" to interfering gases which almost always occur in practice in the gas to be measured or analyzed, the infrared absorption bands of which at least partly overlap those of the gas component for which the analysis is made. This interfering effect is decreased or softened to a degree in the known devices by the use of the receiving layers disposed in succession, but is not completely eliminated because of the variable lengths of the layers. This residual interference effect may make the use of the infrared gas analysis devices in some case, particularly where good selectivity is of importance, impossible. It has been known that the cross-sensitivity effect may be eliminated by suitable radiation filters. However, the use of such filters simultaneously reduces the sensitivity of the device. As a result of the amplification which must be increased when sensitivity is reduced, other interference effects gain in importance and, in addition, the filters show a considerable temerature effect. Moreover, the radiation filters add to the cost of the apparatus.
Even in these devices, zero-drifts may still occur, despite the basically good zero point character. In order to eliminate these zero-drifts, apparatus have been known by which the zero point is controlled and possibly automatically adjusted at certain intervals, either fixed or at intervals to be selected by the operator.